The invention concerns a hybrid gas generator for safety systems in road vehicles. It consists of an initial container for compressed gas which is closed by a bursting diaphragm,
a second container with a combustion chamber and an electrically ignitable propellant system, whereby PA1 the second container includes a propellant gas outlet sleeve, which contains a movable piston as the means of destroying the bursting diaphragm.
Such a hybrid gas generator is known from PCT application WO 93/11 973, whereby the movable piston in a propellant gas outlet sleeve is designed as a hollow piston. This hollow piston is fixed in a central bore in the propellant gas outlet sleeve such that several shearing bolts are led perpendicular to the movement direction of the piston through the propellant gas outlet sleeve into the wall of the hollow piston. When the propellant is ignited, the hollow piston is accelerated by the generated propellant gas towards the bursting diaphragm on the compressed gas container whilst shearing the aforementioned shearing bolts. The hollow piston and the propellant gas outlet sleeve are designed so that the hollow piston becomes trapped in the central bore of the propellant gas outlet sleeve when it has pierced the bursting diaphragm on the compressed gas container. The face of the hollow piston which faces the propellant system is closed by a bursting diaphragm, which is only destroyed when the pressure built up in the combustion chamber is sufficient to shear the bolts. The pressure required for this is set by appropriate arrangement of the bursting diaphragm which closes the hollow piston, in particular with the help of predetermined breaking points.
In this above-mentioned document, an additional hybrid gas generator is described, in which the hollow piston for destroying the bursting diaphragm on the compressed gas container is not fixed by shearing bolts to the central bore of the propellant gas outlet sleeve, but instead uses another diaphragm. This bursting diaphragm, which is designed as a disk, closes off the face of the propellant gas outlet sleeve closest to the propellant system and is fixed to it by welded connections. At the same time the face of the hollow piston is also fixed to this bursting diaphragm by means of welded connections. The pressure which destroys this disk-shaped bursting diaphragm is also set by an appropriate arrangement of predetermined breaking points.
The hollow piston and the propellant gas outlet sleeve which contains this hollow piston are designed so that only part of the lateral surface area of the piston is in contact with the inner wall of the central bore. In fact, it is only the end of the lateral surface of the hollow piston adjacent to the propellant system which has a diameter corresponding with the diameter of the central bore of the propellant gas outlet sleeve. In addition a further contact area has been created at the opening of the propellant gas outlet sleeve which is opposite the bursting diaphragm of the compressed gas container, whereby its diameter is limited to that of the hollow piston. The disadvantage of this is that there is no stable guide system for the hollow piston in the propellant gas outlet sleeve.
A further disadvantage of known hybrid gas generators is that a complicated, multi-part construction is necessary both for the propellant gas outlet sleeve as well as for the moving piston, in particular a further bursting diaphragm is required which ensures the correct pressure for the movement of the hollow cylinder.